1. Technical Field of the Invention
The present invention relates broadly to the field of apparatuses and methods for measuring intracranial pressure.
2. Related Art and Problems to be Solved
Monitoring intracranial pressure (ICP) is of significant diagnostic and post-operative importance for patients with cranial injuries, pathologies, or other conditions that may affect the pressure of the subarachnoidal fluid around the brain, and for patients who have undergone brain surgery.
Many known methods and techniques are invasive and thus, can be very painful, and possibly harmful to the eardrum. Other known methods require absolute calibration which can require bolus injection into the column surrounding the spinal cord, head titling procedures, and determination of blood volume input and output. Some of these requirements are impractical and invasive. Still other known techniques and apparatuses use ultrasonic power, which may be harmful to the patient, in conjunction with extensive algorithms. Furthermore, the accuracy of many of the known algorithms as well as the analysis of the ultrasonic waveforms can be questionable.
Accordingly, it is an object of the present invention to provide a method and apparatus for measuring ICP that solves the problems and cures the deficiencies of the prior art methods, apparatuses and techniques.
Other objects and advantages of the present invention will in part be obvious and will in part be apparent from the specification.
The present invention is directed to a method and apparatus for measuring intracranial pressure. In at least one embodiment, the instrument can utilize two signals, information and reference, to produce an accurate measurement of changes in ICP. The information signal can include the sum of changes in ICP due to changes in average cranial pressure and changes due to the expansion and relaxation of blood vessels within the brain. The reference signal is taken from a point on the body where the signal consists of essentially changes in blood pressure only. The reference signal gives one the ability to calibrate the information signal because the pulsatile component of the information signal is a scaled replica of the reference signal.
In at least one embodiment, the method comprises the steps of generating an information signal that comprises pulsatile components that are related to intracranial pressure and blood pressure, generating a reference signal comprising pulsatile components that are solely related to blood pressure, processing the information and reference signals to determine the pulsatile components of the information signal that have generally the same phase as the pulsatile components of the reference signal, and removing from the information signal the pulsatile components determined to have generally the same phase as the pulsatile components of the reference signal so as to provide a data signal having pulsatile components wherein substantially all of the pulsatile components are related to intracranial pressure.
In at least one embodiment, the apparatus of the present invention comprises an apparatus for measuring changes in intracranial pressure, comprising a first measuring device for generating an information signal that comprises components (e.g. pulsatile changes and slow changes) that are related to intracranial pressure and blood pressure, a second measuring device for generating a reference signal comprising pulsatile components that are solely related to blood pressure, a processor for processing the information and reference signals to determine the pulsatile components of the information signal that have generally the same phase as the pulsatile components of the reference signal, and a circuit for removing from the information signal the pulsatile components determined to have generally the same phase as the pulsatile components of the reference signal so as to provide a data signal having components wherein substantially all of the components are related to intracranial pressure.